An anticancer agent goes through the whole body via the bloodstream when it is administered to a patient, and damages not only cancer tissues in which the cell proliferation is active, but also normal cells whose proliferation is active, such as normal small-intestinal mucosa, bone marrow, or hair root cells, and therefore, side effects occur in some cases.
In order to suppress the side effects, a drug targeting therapy in which an anticancer agent can specifically act on cancer tissues, a so-called drug delivery system (DDS), has been contemplated. As one of the methods, there is a method in which a cancer-specific antibody is bound to an anticancer substance or the like, and the anticancer substance is specifically accumulated in cancer tissues. However, with this method, even if the anticancer substance is accumulated on the cancer tissue surface, the anticancer substance is bound to a large antibody, and therefore, the anticancer substance is unlikely to be incorporated into cancer cells and its effect is limited. The development of not only an anticancer agent, but also a medicinal agent which has a high desired effect but less side effects has been in demand.
On the other hand, a rhabdomyosarcoma is a malignant soft tissue tumor, which is found in children and young people, and in which cells differentiating into striated muscle undergo malignant transformation, with the following three histopathological types: embryonal rhabdomyosarcoma, pleomorphic rhabdomyosarcoma, and alveolar rhabdomyosarcoma have been reported. Such a rhabdomyosarcoma responds poorly to chemotherapy, and particularly, the malignancy of alveolar rhabdomyosarcoma is high, and there has been a demand to establish a treatment method therefor. It has been reported that this rhabdomyosarcoma incorporates serotonin (see NPL 1 and NPL 2).